Compensating spring



Patented Nov. 16, 1937 PATENT OFFICE comnnsa'rmo sramc mderick P. Flags, Waltham. Masa, assignor to Waltham Watch Company, Waltham, Masa, a corporation of Massachusetts No Drawing. Application August 18, 1934, Serial No. 740,432

2 Clalma, (01. 58-114) This invention relates to springs-so constituted that their strength varies with temperature changes in a manner to neutralize in greater or less degree the effects of temperature on the 5 systems which they control. An important field for such springs is in the escapements of watches, wherein the use of a compensating hairspring enables a balance wheel having a continuous monometallic rim to be used in place of the more delicate and expensive. compensating balances provided with a divided bi-metallic rim. The

practical advantage and economy of using a continuous balance with a hairspring which is so affected by temperature changes as to compensate for changes in the inertia of the balance, due to its expansion or contraction under the same temperature changes, has long been recognized by watch makers; and hairsprings have been produced in the past which effect such compensation with substantial success. Alloys of iron, nickel and other metals have been discovered which, when made into hairsprings, have increasing strength, or modulus of elasticity, with increase of temperature approximately sufficient to compensate for the simultaneous increase in moment of inertia of the balance, and vice versa, within the range of'temperatures to which watches may be ordinarily exposed. But springs made of such alloys are deficient in hardness. Their limit of elasticity is too low, wherefore they are too easily bent out of shape in handling. When given a permanent distortion by being bent or twisted beyond the elastic limit, they are spoiled for practical purposes. Earnest and extensive attempts have been made to improve compensating hairsprings in this respect, but the best products heretofore obtained are much softer than harderred and tempered steel.

The object which I have sought and attained 4 by the present invention has been principally to improve and increase the hardness (or elastic limit) of compensating hairsprings and the like. In carrying this object into effect I have discovered a new alloy from which I have produced 45 hairsprings of a hardness approximately equal to that of the commonly used watch hairsprings made of hardened and tempered steel, and having adequate compensating characteristics.

My improved compensating spring is made from 50 an alloy of ferro-nickel and other metals, having preferably the following composition:-

50 Although the foregoing specific composition is the best for my purpose which I have found after long study and extensive experimentation, my claim to protection is to be construed as em bracing variations in the ingredients thereof and the proportions of such ingredients, within limits 6 hereinafter indicated.

It will be noted that no carbon is included in the foregoing composition. In fact the substantially complete absence of carbon is an important characteristic of the composition, for I have 10 found that carbon is a disturbing element which, if present, introduces unpredictable and variable properties into the springs. Hence the ingredients are provided in refined condition and as pure as possible; and the alloy is treated in the 15 course of its manufacture into springs in such fashion as to eliminate so far as possible any traces of carbon which may be associated as an impurity with any of the ingredients.

In making the alloy, the ingredients are melted 20 together in a suitable furnace, preferably an electric furnace heated by high frequency current. The melt is cast in an ingot of any dimensions suitable for subsequent working. After solidifying, the ingot is annealed in an oxygen 25 free atmosphere; preferably an atmosphere of hydrogen to assist in removal of any traces of carbon which may be present, as well as to avoid oxidizing any of the metals. All necessary subsequent annealings in the course of reducing the 3 ingot to wire of the dimensions suitable for hairsprings are also carried out in an atmosphere of hydrogen, or equivalent of hydrogen, for the same reasons.

The steps of reducing the ingot by swaging 35 and/or drawing to wire, and rolling the wire into ribbon form of required dimensions and shape are performed in any known or other suitable way, the procedure not being a feature of the present invention. It may be noted, how- 40 ever, that the final stages of drawing the wire to its ultimate diameter from a diameter approximately five times as great, and rolling of the ultimate wire into a flat ribbon, are performed cold and without intermediate annealing in order to acquire the maximum hardness obtainable by cold working. Lengths of the ribbon sufilcient for springs of given characteristics are coiled into flat spirals to form the springs and are set, and further hardened, by heat treatment at a suitable temperature and for a suitable length. of time to effect permanence of form.

Hairsprings made as thus described have satisfactory compensation properties. In addition they have much greater hardness than any compensating springs of the prior art. They can be handled in the normal manner employed in assembling and repairing watches without danger of damage from permanent distortion.

The comparative elastic strength of flat spiral 5 springs of this type can be determined by weighing the load which causes permanent distortion of the spring when hung from the collet at the inner end of the spring while the outer end is clamped in a fixed position. Such a comparison between a spring made according to this invention and a standard steel hairspring for the ,same duty showed that a load of 4.5 grams was required to make a permanent distortion in my spring, while a load of, t.8 grams caused a per-- manent distortion in the steel spring. Springs according to this invention therefore are substantiallyequal in hardness, or elastic limit, to steel springs. They are nearly 30% superior in this particular to the best compensating hairsprings on the market and better than another type of spring which has been extensively used commercially.

I have ascertained that the hardness of my springs is due to the association of silicon and manganese in the alloy. If either manganese or silicon is present without the other, the hardness resulting from cold drawing of the wire is less at the maximum than in alloys containing both silicon and manganese; and such hardness is lost to a large extent by the heat treatment employed in setting the springs.

I have found further that manganese has a sensible eifect on the temperature compensation of the spring, its influence being much greater than that of silicon in that respect; that its content should be as much as 2%; and that larger quantities of manganese give increasing hardness, but that a content greater than 6% is not 1 desirable.

As to silicon, the optimum content seemsto be 4%. Larger contents give no apparent advantage, although some excess is unobjectionable. Lesser contents down to 3% are nearly as satisfactory; but when less than 3% is present, the hardness due to cold working is diminished.

The small proportion of titanium in the illustrative formula hereinbefore given is not essential to the success of the invention, but is a desiraoaea'm able factor to increase the ease of working the metal. It is the residue of a larger quantity supplied before melting, which, owing to the high aflinity of titanium for oxygen, is useful during the melting process as an agent for deoxidizing the other metals. Nickel and chromium are previously known ingredients of compensating springs, which I have incorporated, and the quantities or proportions of which I may vary in accordance with pro-existing knowledge in the art. t

The foregoing description and discussion of hairsprings for watches is not to be understood as a limitation of the invention to such springs exclusively. On the contrary I claim protection for springs of all characters and for all purposes, which may be made of the composition herein described with useful efiect.

What I claim' and desire to secure by Letters Patent is:--

l. A spring having a high elastic limit and variable modulus of elasticity at different temperatures within normal atmospheric limits of temperature, consisting of an alloy containing a content of nickel between 30% and 40%, a content of chromium between 3% and 12%, a content of manganese of at least 2% and not over 6%, a content of silicon between 1% and 6%, and the balance iron.

2. A spring having a high elastic limit and variable modulus of elasticity at different temperatures within normal atmospheric limits of temperature, consisting of an alloy having substantially the following composition:

Per cent Nickel 86 Chromium 4. 5

Manganese 3 Silicon 4 Titanium 0. 1

Iron the remainder ERICK P. FLAGS. 

